Air-space insulated conductor



March 5, 1946. H D [SENBERG 2,395,872

AIR-SPACE INSULATED CONDUCTOR.

Filed May 22, 1943 INVENTOR. [757/13 D. 15c film/Y] aux/v w i f-2a Patented Mar. 5, 1946 UNITED STATES PATENT: OFFICE Ara-space 1x53331 11 counuc'roa Appllcatlo: :2; :31. 487,990

This invention relates to low capacity low losselectric cables, and is particularly concerned with a cable comprising an air-space insulated conductor which is supported within an outer sheath in coaxial position relative thereto.

Prior cables of this general type employ expedients, e. g., perforated axially spaced disks for holding the inner conductor centrally within the outer sheath. Such structures areusually made in sections and these sections are assembled to form the cable. Attempts made in the past to manufacture such cables in continuous production processes have apparently not been successful:

The centering or radial spacing of the central conductor, in a continuous production process is made possible, in accordance with the present invention, by winding or braiding the outer sheath, and simultaneously winding an elastic insulating-member so as to form successive groups or series of open helices which are substantially larger than the diameter of the inner conductor, for engagement with the inner wall of the outer sheath, and alternately forming turns which are tightly wound around the inner conductor for the purpose of holding it in air-space insulated relation substantially centrally within the sheath.

Some embodiments of the invention are described below in connection with an example of a coaxial cable, sections ofiwhich are diagrammatically shown in the accompanying drawing. In the drawing, I

Fig. 1 illustrates part of a coaxial cable in longitudinal section, showing the outer sheath and the new helically wound conductor-supporting and conductor-spacing member in the interior thereof;

Fig. 2 represents a transverse section taken along lines 2-2 through the structure shown in Fig. l; and

Figs. 3 and 4 are diagrams intended for explanatory purposes in connection with the description oi a modification.

Reference numeral ll indicates the outer sheath. This sheath may be made of braided or wound conductive material and constitutes, in

this embodiment, the outer conductor of the structure. The braiding or winding of the sheath I may be accomplished in'accordance with known and approved manufacturing processes. The new helical conductor-supporting and conductor-spacing member consists in this embodiviously mentioned axially successive groups or series of large helices l2, l3, l4, l5, eachgroup comprising a plurality of open turns and each helix having an outer diameter which corresponds to the inner diameter of the sheath I l, and small alternate turns l6, 11, "each of which is wound around the central conductor l9. These latter conductor holding means are shown as comprising single turns; several turns may be provided in each instance or in some instances, if desired. The continuous elastic strip is thus wound on the inner conductor at axially spaced points thereof. and the outer sheath or conductor is continuously coaxially wound or braided on the open helices of the strip so as to form a continuous tubular outer structure.

The process of producing the new cable requires progressive feeding of the continuous central conductor, as well as the feeding and helical winding of the continuous supporting and spacing strip, and also the feeding and braiding or winding of the material forming the continuous outer conductor or sheath. Machines which; are suitable and adapted for simultaneously executing and properly coordinating these operations in relation to each other are known. The outer sheath may be provided with a protective covering if desired.

The outer tubular conductor may be composed of conductive strip, tape or foil material which is progressively wound to form the continuous tubing structure, or of conductive strands which are for this purpose progressively braided. The

sheath may also be composed of a wound or braided structure comprising conductive members as well as members or insulating material, The conductive members will then furnish the con ductive continuity and together with the insulating members, they will form the sheath. Desired variable degrees of flexibility of the cable will be obtained by utilizing the latter structure where the operating conditions or other requirements of the final product permit or indicate its use.

The helically wound supporting and spacing strip may be made of phenolic resins, methyl methacrylate resins, vinyl chloride acetate resins, polystyrene resins or polyvinyl chloride resins. These materialsare mentioned merely for the purpose of giving examples; numerous other suitable substances are known.

It is assumed, in the embodiment shown in Figs. 1 and 2, for reasons of convenient representation, that the elastic strip forms between the groups of large helices l2, I3, II, I! radially extending curved strip sections which connect with the turns it, ll, 18, and which are disposed in axially successive substantially identical angular planes, e. g., the angular plane taken by the strip sections l3 and H shown in Fig. 2. The centering forces exerted by these radially extending strip sections include pressure in substantially identical angular directions, and counter or compensating pressure, produced by the elastic structure of the material, which is eflective in opposite directions. The angular forces are thus at each axially successive point similarly distributed and hold the conductor I9 substantially centered within the tubular outer sheath.

To describe the structure in a more specific fashion; the axial spacing between the strip portions at the covering I! in the groups l3, I4, and I (Fig. l) is greater than the axial spacing of the strip portions nearer the conductor 19 in the intermediate sections or portions identified by the reference characters IE, IT and H3. The flat insulating strip in this structural arrangement provides elasticity, and provides support for the conductor IS in the complete cable.

Such a structure requires, however, that the elastic strip is made substantially uniform throughout its length or, conversely, that it is put in position substantially uniformly during the winding operation so as to produce the required uniform angularly effective compensating forces at all axially spaced points where engagement is made with the central conductor.

Figs. 3 and 4, taken together with Fig. 2, indicate an alternative manner of disposing the radial strip sections forming the successive turns on the central conductor. The sections forming the turn ll (Fig. 2) are angularly displaced with respect to the sections forming the preceding turn l6 (Fig. 3), and the sections forming the succeeding turn l8 (Fig. 4) are angularly displaced with respect to the preceding turn H. The radial strip sections forming the remaining conductorholding turns in the cable structure are similarly disposed in axially progressively different angular positions. I

The radially efiective elastic forces of each pair of the radially extending strip sections which connect the various conductor-holding turns with the adjacent groups of open helices are in the second embodiment similar to those described in connection with the first embodiment; that is, they tend to center the inner conductor at each point of engagement with the elastic spec ing strip. The various strip sections are, in the second embodiment, in addition axially successively angular displaced so as to produce axially effective angularly operating compensating forces to balance and to equalize slight variations in the strip material that might result from manufacturing tolerances or variations that might occur incident to the winding of the elastic strip. The inner conductor is again held in a positive manner centrally within the tubular sheath.

Changes may be made within the scop and spirit of the following claim, in which I have defined what I believe is patentable and what I desire to have protected by Letters Patent of the United States.

I claim as my invention:

An air-insulated cable comprising in combination a continuous electrical conductor, a tubular outer covering, and insulating means supporting said conductor centrally within said covering and spacing the same therefrom, said insulating means comprising flat insulating strip having elasticity and with axially successive but separated groups of helical convolutions arranged fiatwise relative to the inside surface of and in contact with said outer covering, said strip having a portion intermediate each two groups of helical convolutions comprising a single complete turn directly supporting the conductor and helically disposed thereon, with the opposite ends of the intermediate portions each merging in a gradual curvature with the end of an adjacent correspond- 40 ing helical convolution of a, group, the axial spacing of the insulating strip adjacent the outer covering being greater than that of the intermediate portion next to the central conductor.

HANS D. ISENBERG. 

